Method of producing a mercurycalomel electrode



United States Patent 3,409,517 METHOD OF PRODUCING A MERCURY- CALOMEL ELECTRODE Serafim Fedorovich Zavgorodny, Budennovsky, Prospect 70, Apt. 2, and Ivan Fedotovich Kamyshnikov, Prospect K. Marxa 55, Apt. 6, both of Rostov-na-Donu, U.S.S.'R. No Drawing. Filed May 11, 1965, Ser. No. 454,960 Claims. (Cl. 204-29) ABSTRACT OF THE DISCLOSURE A mercury-calomel electrode is produced by calcinating a graphite rod, washing the graphite rod with water, coating the graphite rod with a layer of mercury and calomelby electro-chemical deposition thereof from a solution of Na (HgCl at a potential of 1.3 to 1.7 volts and thereafter immersing the coated graphite rod in solution of potassium chloride.

The present invention relates to a method of producing a mercury-calomel electrode, Such electrodes are used in potentiometric titrations and also for the determination of the pH of solutions.

There is a well-known method of producing the mercury-calomel electrode according to which platinum wire soldered in a glass tube is immersed into a vessel filled with mercury. On the mercury surface there is placed a layer of specially prepared mercury-calomel paste, and then the vessel is filled with a saturated solution of potassium chloride.

The equilibrium potential of this electrode is stabilized in approximately two days.

The disadvantages of this well-known method reside in the complex and lengthy technology for producing mercury-calomel electrodes which requires the use of highly purified mercury as well as the preparation of a mercury-calomel paste by mixing metallic mercury with calomel. This method also requires the use of costly platinum.

The object of this invention is to provide a method which allows a reduction in the time required for producing the mercury-calomel electrode, replaces costly platinum with a cheaper material and obviates the necessity of using highly purified mercury.

According to the above-mentioned object, the method of the invention consists in coating a graphite rod with a layer of calomel and mercury, which mercury is electro- 3,409,517 Patented Nov. 5, 1968 ice composition. The said composition is prepared by dissolving mercury chloride in a saturated solution of sodium chloride.

The graphite rod is first calcinated in a burner flame, then washed into hot distilled water and cemented in a glass tube, in which a small amount of metallic mercury is placed to provide contact with an external circuit.

The electrolysis is caried out at a potential of 1.3 to 1.7 v., preferably at 1.5 v. for 25-30 minutes, and then the graphite rod is washed with distilled water. To increase the strength of the calomel and mercury layer deposited on the graphite rod, the latter is coated with a layer of collodion diluted in ester in the ratio of 1:3 and then immersed in a saturated solution of potassium chloride.

Another method of stabilizing the electrode consists in immersing the electrode in a hot 2 percent solution of agar-agar, prepared on the basis of a saturated solution of potassium chloride.

The values of the potentials obtained for the mercurycalomel electrode prepared according to the present method, as compared with those of the known mercurycalomel electrode, as well as the data confirming the stability and reproducibility of the graphite-calomel electrode are given in Tables 1 and 2.

Example 1 First an electrolyte is prepared by dissolving 7.2 g. of NaCl in 20 ml. of water and adding 0.66 g. of HgCl thereto. Then the thusly prepared solution is diluted with distilled water in the ratio of 1:2. A graphite rod, 1.5 mm. long, is placed into the thus prepared electrolyte. The graphite rod is precalcinated in a burner flame to remove adhesives, washed in boiling distilled water for 2 hours, dried and a part of the rod is cemented in a glass tube, in which a small amount of metallic mercury is placed in order to provide contact with an external circuit. Then the exposed part of the rod is immersed in the prepared electrolyte at a temperature, of 60 C. in order that electrodeposition may be eifected.

In the electrodeposition, a platinum rod is used as the anode, while the graphite rod serves as the cathode. The electrodes are coupled to the poles of a DO. source with a potential of 1.5 v. p

The electrolysis is carried out for 20-30 minutes with stirring. Then the graphite rod is carefully washed in distilled water at room temperature and dried.

The dry electrode is then coated with a layer of collodion dissolved in ester and then immersed into a satchemically deposited from an electrolyte of a Na (HgCl urated solution of potassium chloride.

TABLE 1.-RESULTS OFCDETE RMINING pH WITH VARIO US GRAPHITE TABLE 2.DETERMINATION OF pH Electrodes Method of measurement Serial Testing Temper- Electrolyte Potential, Difierencc, pH Difier- N 0. day aturc, Graphite, Quinhydrone Hydrogen mv. rnv. ence, mv.

C. Calomel mercuryealomel saturated 1 1st 22 Caloniel Quin Acetate bufier 183 4. 62 0 G.M.C.S.. Quin solution. 183 4. 62

Acetate bufier 183 0 4. 62 0 solution. 183 4. 62

3 3rd 25 CalomeL- G.M.C.S Quin }Bufier solution, 368 1 1.43 0.02

Quin. pH 1.4. 367 1. 45

4 3rd 25 CalomeL. G.M.O.S. Quin }Bui1er solution, 334 1 2.01 0.02

Quin pH 2.0 335 1.99

3rd 25 Calomel Quin }Bufier solution, 1.04 0 4. 38 0 G.M.C.S. Quin pH 4.3. 1. 94 4.38

6 3rd Calomel.. G.M.C.S Quin }Bufier solution, 126 0.5 5.53 0.01

Quin pH 5.5. 126.5 5.52

7 3rd 22 CalomeL. G.M.C.S Quin }Bufier solution, 2O 2 8.10 0.01

G.M.C.S Quin pH 8.1. 18 8.00

8 4th 25 Calomel Quin }Bufier solution, 38 0 7.02 0

G.M.C.S Quin pH 7.0. 38 7.02

9 6th 25 Calomel Quin }Bufier solution, 320 0 2.25 0

G.M.C.S. Quin pH 2.3. 320 2.25

7th CalorneL Hyd }Bufier solution, 744 0 8. 43 0 G.M.C.S pH 8.4. 744 8. 43

11 7th 24 Calomel Hyd }Bufier solution, 800 1 947 0.01

G.M.C.S pH 9.4.7. 805 946 12 7th 25 CalomeL Hyd }But;{er1so5l 1tion, 3 0.05

13 7th 25 Calomel. Hyd }Bufier solution, 937 0 11.70 0

G.M.C.S pH 11.70. 937 11. 70

14 10th. 22 }Bufler solution, 261 1 3.29 0.02

15 11th 22 }BuiITaer7 solution, 0 0

We claim: with a saturated solution of sodium chloride in a weight 1. A method of producing a mercury-calomel electrode comprising calcinating a graphite rod, washing the calcinated graphite rod, coating the washed, calcinated graphite rod with a layer of mercury and calomel by depositing the coating electrochemically from a solution of ratio of about 1:10 and thereafter diluting the mixture by addition of water in an amount twice that of the mixture,

5. A method as claimed in claim 1 wherein the coating is deposited electro-chemically for a period of 20-30 minutes at a temperature of about C.

References Cited UNITED STATES PATENTS 3,006,821 10/1961 Haring 20456 OTHER REFERENCES Ives et al.: Reference Electrodes, 1961, pp. 128-137.

HOWARD S. WILLIAMS, Primary Examiner.

T. TUNG, Assistant Examiner. 

